Blender Git Loki

WIP cache system for filebrowser entries.

Core part seems to be working, but this is still heavy WIP, much to do
to resume complete features from existing code. Mainly:

* Previews (those should only be ran on cached items now).
* Use block-caching to load in-display entries.
* Rework things like selection (cannot store selected states in entires anymore).

Also, internal listing is stupid currently (since it still stores everything
as FileDirEntry & co), not really crucial currently, but ultimately it'll
use its own, compact struct to keep full listing!

Also did some minor cleanup/renaming.